The present invention relates to a method for adjusting a preset desired state of charge of an electric energy accumulator of a vehicle, in particular a hybrid vehicle, while traveling uphill and downhill.
Hybrid vehicles utilize a complex operating strategy, according to which the electronics control the operating states, in which the vehicle is driven purely by use of the internal combustion engine, the internal combustion engine with the assistance of the electric machine or optionally purely by use of the electric machine. In terms of the management level, the control of the state of charge for the electric energy accumulator is located “below” the operating strategy. In simple terms, a desired state of charge is determined (or rather defined) as the reference value, and the actual state of charge is adjusted on the basis of this desired state of charge.
The object of the invention is to provide a method for adjusting a preset desired state of charge of an electric energy accumulator of a vehicle while traveling uphill and downhill.
This object is achieved by a method for adjusting a preset desired state of charge of an electric energy accumulator of a vehicle, in particular a hybrid vehicle, while traveling uphill and downhill. The method includes the acts of: determining whether the condition for a vehicle traveling uphill or downhill is met according to a preset decision logic; determining whether an actual state of charge of the energy accumulator lies within a preset range of the state of charge; and adjusting the desired state of charge according to a preset adjustment logic, if (i) the condition for a vehicle traveling uphill or downhill is met, and (ii) the actual state of charge of the energy accumulator lies within the preset range of the state of charge. Advantageous embodiments and further developments of the invention are described herein.
The starting point of the invention is a method for adjusting a preset desired state of charge of an electric energy accumulator of a vehicle, in particular a hybrid vehicle, while traveling uphill and downhill.
The term “desired state of charge” refers to that state of charge, with respect to which the actual state of charge of the energy accumulator is to be adjusted. The actual state of charge can lie both below and also above the desired state of charge.
The term “energy accumulator” is to be given a broad interpretation. It comprises, in particular, batteries (or rather accumulators), as found in conventional vehicles, in hybrid vehicles or also in purely electric vehicles. However, the term “energy accumulator” is not restricted to batteries or accumulators, but also includes other kinds of electric energy accumulators, such as capacitors, in particular so-called “super-caps.”
The above-introduced concept “hybrid vehicle” includes vehicles, the drive train of which exhibits an internal combustion engine and at least one electric motor that generates a boost. In this context it can involve so-called “full hybrids” as well as also so-called “mild hybrids.” A “full hybrid” may be driven by choice purely by use of the internal combustion engine, the internal combustion engine with the assistance of the electric machine or purely by use of the electric machine, whereas a mild hybrid may be driven only by use of the internal combustion engine or, by choice, the internal combustion engine with the assistance of the electric machine.
In accordance with the invention, the desired state of charge should be adjusted while traveling uphill or downhill in such a manner that when the vehicle is traveling downhill, the energy accumulator is adequately capable of consuming energy—that is, the potential energy that is liberated during the downhill descent can actually be recuperated—that is, can be converted into electrical energy and can be stored in the energy accumulator.
Working on this basis, the control unit is configured such that, for example, on reaching a transitory altitude, sufficient charge capacity is reserved, so that during the subsequent downhill descent, the potential energy that is liberated can actually be recuperated. Expressed in simple terms, the desired state of charge should be adjusted, in such a manner that the actual state of charge of the energy accumulator in the region of the local maxima of a gradient profile is relatively small, so that then the energy that is liberated during the subsequent downhill descent can actually be recuperated.
According to the invention, the first step is to determine in accordance with a predefined decision logic whether for the purpose of the decision logic the condition for uphill travel or downhill travel is even satisfied. Furthermore, it is determined whether the actual state of charge of the energy accumulator lies within a predefined state of charge range. For example, a state of charge range can be defined between 40% and 70% of the maximum capacity of the energy accumulator. Such a range with a lower limit and an upper limit is typically specified as the main operating range for batteries, in particular accumulators, because operating the energy accumulator below the lower limit and/or above the upper limit of this range would significantly shorten the service life of the energy accumulator.
According to the invention, the desired state of charge is adjusted in accordance with the predefined adjustment logic, if the predefined adjustment logic detects that the condition for a vehicle traveling uphill or downhill is satisfied, and if, in addition, the actual state of charge of the energy accumulator lies within the preset range of the state of charge.
The invention provides that the desired state of charge is raised above a “normal” desired state of charge, if the condition for a vehicle traveling downhill is met. On the other hand, the desired state of charge is dropped below a “normal” desired state of charge, if the condition for a vehicle traveling uphill is met. The result of this logic is that there is an adequate charge capacity on hand during the downhill descent, in order to be able to convert the potential energy that is liberated during the downhill descent into electrical energy and to be able to store this energy in the energy accumulator.
The normal desired state of charge can lie, for example, in a range between 50% and 70%, preferably approximately 60% of the maximum capacity of the energy accumulator.
According to a further aspect of the invention, the gradient of the increase and/or decrease in the desired state of charge is a function of the inclination and/or the downward slope of the distance “last” covered—for example, a predefined traveled section of the road. Thus, for example, a section of road of several hundred meters or just a few kilometers can be considered.
A further aspect of the invention provides that the decision logic for determining whether the condition for a vehicle traveling uphill or downhill is met evaluates an altitude signal and/or inclination signal. In this case, it can involve an absolute altitude or inclination signal or also a relative altitude or inclination signal. The term “absolute” is defined as, for example, monitoring the altitude above the sea level. As an alternative, the altitude or rather the change in altitude since the last engine startup or the like could also be monitored. As an alternative, the absolute inclination or rather the absolute gradient of the distance covered can also be evaluated.
The absolute or relative altitude and/or inclination signal can be obtained, for example, by measuring the ambient air pressure. Modern vehicles with internal combustion engines are generally already equipped with an air pressure sensor, because the ambient air pressure is an important input parameter for controlling the fuel injection. Thus, it would be possible to use the air pressure or rather the “altitude signal” that is already present in the vehicle in any event.
As an alternative or in addition, an altitude signal could also be obtained from the data that are delivered by a navigation system that, for example, is permanently integrated into the vehicle.
As an alternative, an “inclination signal” could be determined from the rolling resistance moment—that is, from the drive torque and/or the vehicle acceleration that occurs during this drive torque, so that in this case, for example, an estimated and/or average vehicle weight can be used for the calculation. Then, an altitude signal could be derived from the wheel resistance integrated over the distance traveled.
As an alternative or in addition, a pitch angle—that is, the inclination angle of the vehicle with respect to the horizontal plane—could also be evaluated. From this evaluation, an inclination signal could be derived, from which in turn an altitude signal can be generated through integration.
According to a further aspect of the invention, a mean altitude gradient is formed from the absolute or relative altitude and/or inclination signal. At the same time, the time frame, during which this gradient is determined, can be freely adjusted. As a result, the altitude gradient represents the altitude differential, over which the vehicle was moved within the given time frame.
This can happen, for example, by forming a first signal and a second signal from the absolute or relative altitude and/or inclination signal. The first signal reflects the time based or distance based changes in the altitude and/or inclination in an unfiltered manner or in a slightly filtered manner. The second signal reflects the time based or distance based changes in the altitude and/or inclination in a more filtered manner than the first signal. In this context “more filtered” means that the actual changes in the inclination of the stretch of road, on which the vehicle is currently traveling, and/or the actual changes in the altitude of the vehicle, are reflected slightly attenuated or delayed in time in the second signal, whereas the changes in inclination and/or the changes in altitude are mapped in the first signal in a manner very much like the actual gradient profile of the road.
It can be provided that the condition for a vehicle traveling uphill and/or downhill is detected, only if the amount of the difference between the two signals exceeds a preset value.
An additional embodiment of the invention provides that the increase and/or decrease in the desired state of charge is a function of the amount of the difference between the two signals.
Furthermore, the invention includes a method for controlling the actual charge state of an electric energy accumulator of a vehicle. This method specifies the desired state of charge as the reference value that is determined according to the above-described method.
Other objects, advantages and novel features of the present invention will become apparent from the following detailed description of one or more preferred embodiments when considered in conjunction with the accompanying drawings.